Diversey Harbor Lake Water Temperature
Diversey Harbor Lake in Cook County, Illinois averages about 67°F at the surface in summer — warmest in Sep (~73°F) and coldest in Nov (~56°F). These are typical values by month, not a live reading.
Typical water temperature by month
Typical surface water temperature by month, from 13 field readings (2013–2023) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is Diversey Harbor Lake warm enough to swim?
Brisk but swimmable for short dips — most people acclimate after the first few minutes.
Want more than temperature? Diversey Harbor Lake scored A on water quality — clarity, algae, phosphorus, depth, fish species, and swimming safety, all on one report card.
Water temperatures at nearby Illinois lakes
Summer average ~76°F
Summer average ~78°F
Summer average ~78°F
Summer average ~69°F
Summer average ~75°F
Summer average ~78°F
Explore water temperatures
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Frequently asked questions
What is the water temperature of Diversey Harbor Lake?
Diversey Harbor Lake has a typical summer surface temperature of about 67°F. It is usually warmest in September (around 73°F) and coldest in November (around 56°F). These are typical values by month from 13 EPA Water Quality Portal field readings (2013–2023), not a live reading.
When is Diversey Harbor Lake warmest?
Surface water at Diversey Harbor Lake is typically warmest in September, reaching about 73°F. Lake surface temperature lags air temperature by several weeks, so the warmest water usually arrives in mid-to-late summer even though the hottest air can come earlier.
Is Diversey Harbor Lake warm enough to swim?
At its typical summer peak of about 67°F, Diversey Harbor Lake rates as "cool" for swimming. Brisk but swimmable for short dips — most people acclimate after the first few minutes.
Where does this Diversey Harbor Lake water temperature data come from?
Every temperature on this page is a typical (climatological) value computed from real surface-water field readings collected by state and federal agencies and published through the EPA Water Quality Portal — 13 readings from 3 monitoring stations between 2013 and 2023. They describe what is typical for each month, not the temperature right now.
About this data
Water temperatures are a climatology — the typical value for each month, averaged from real surface-water field readings collected by state and federal agencies and published through the EPA Water Quality Portal. They tell you what to expect, not the temperature at this moment. Actual conditions vary with recent weather, depth, and time of day.